A hybrid vehicle comprises an internal combustion thermal engine, which transmits torque to the driving wheels by means of a transmission provided with a gearbox, and at least one electric machine, which is electrically supplied by an electronic power converter mechanically connected to the driving wheels. The electric machine is driven by an electric drive connected to an electric storage system typically consisting of a pack of chemical batteries, possibly connected in parallel to one or more supercapacitors.
A conventional vehicle comprises a thermal engine cooling system, which uses a cooling liquid (typically water mixed with antifreeze substances) which is circulated through the thermal engine and through a water-air radiator which is invested or influenced by the air when the vehicle is moving.
In a hybrid vehicle, a cooling system dedicated to the electric components, i.e. to the electric machine, the electronic power converter and the storage system, is also used or required to avoid the electric components from overheating. With this regard, it is worth noting that, in use, all electric components are sources of electrical energy loss, which is transformed into heat and is to be appropriately disposed of. As in the thermal engine cooling system, the electric component cooling system also uses a cooling liquid (typically water mixed with antifreeze substances), which is circulated through the electric components and through a water-air radiator which is invested or influenced by the air when the vehicle is moving. The two cooling liquids of the two systems (i.e. the cooling liquid of the thermal engine cooling system and the cooling liquid of the electric component cooling system) are kept separate, because the cooling liquid circulating through the thermal engine reaches, at full rate, a temperature of 100°-110° C., while the cooling liquid circulating through the electric components should not exceed, at full rate, a temperature of 65°-85° C.
In order to keep the two cooling liquids separate in the known hybrid vehicles, two independent radiators are provided, arranged side-by-side (typically overlapped so that the radiator of the electric component cooling system is invested or influenced by the air first). In so doing, however, the radiator of the electric component cooling system may not be effectively and efficiently used for cooling the thermal engine when the electric components are not used (e.g. when running on a highway).
Patent application WO2004020927A1 describes a cooling circuit of a vehicle provided with a main high-temperature branch which cools the thermal engine and with a secondary low-temperature branch which cools the vehicle equipment; the two branches share the same radiator which has a central portion which may be alternatively used by the branches acting on corresponding hydraulic valves.